Commercial availability of a safe, inexpensive, noninvasive monitoring device for total body water content and its intracellular and extracellular distribution within individuals could improve the quality of medical care and reduce both the need for invasive monitoring procedures and health care costs. In phase one of this project, we propose to measure total body water, intracellular water and extracellular water as separate fluid compartments by isotopic means in patients with various disorders and simultaneously to study the frequency-dependent impedance characteristics of these individuals. This will establish the relationships between frequency-dependent bioelectric impedance and the partition of total body water into intracellular and extracellular compartments. We will use the information obtained to develop equations permitting bedside estimates of these fluid compartments from the anthropometric and bioelectric data only. In phase two, we will use the relationship established in phase one to conduct a randomized, prospective study to help manage a group of patients, comparing results with a control group, managed by standard clinical evaluation and commonly accepted methods. We will evaluate the overall efficacy of treatment guided by this type of monitoring, the frequency of adverse clinical events, and the cost of care against the same determinants in the control group. A separate phase two study will evaluate the relationships between frequency-dependent bioelectric impedance of the thorax and the magnitude and partition of lung water in a group of critically ill patients. Success in this project will enable development of a new, approved medical device. We have a working prototype bioimpedance device for conducting the Phase I study now.